1. Field of the Invention
The present invention relates to a detecting device and method, especially to an impedance detecting device and method.
2. Description of Related Art
A consumer electronic device is usually equipped with one or more audio output jacks operable to be coupled with one or more sound output devices such as earphones or loud speakers. However, sound output devices in compliance with different specifications provide different output effects in response to the same audio signal, which means that an audio signal may be appropriate for a loud speaker to generate sound at proper volume while an earphone might generate sound at full volume based on the same signal, or an audio signal may be appropriate for an earphone to generate pleasing acoustic effect while another earphone might generate unpleasant acoustic effect according to the same signal. The aforementioned problems exist because an audio codec generating audio signals anticipates an output impedance (i.e. the expected input impedance of some sound output device receiving the audio signals) different from the impedance in reality and thereby outputs the audio signals at overly high or low amplitudes. In order to deal with some sound output device with a higher input impedance (e.g. an active loud speaker, which means that the concerned audio codec will face a higher output impedance) to provide a signal at higher volume, and further tackle some sound output device with a lower input impedance (e.g. an passive loud speaker or an earphone, which means that the concerned audio codec will face a lower output impedance) to provide a signal at lower volume, some known art sets a resistor 130 between an output buffer 110 of an audio codec and an external sound output device 120 in series (as it is shown in FIG. 1), so as to modify the energy of signals from the output buffer 110 to the sound output device 120 by the voltage-consuming property of the resistor 130. However, this solution has at least the following problems. First, if the sound output device 120 suffers from a capacitance or inductance effect, even though the output buffer 110 keeps the amplitude of its output signal stable regardless of the signal frequency, since the capacitance or inductance effect will vary by frequency and contribute to impedance variation, the sound output device 120 will still generate sound at unstable volume due to frequency variation. Moreover, since sound output devices of different specifications are likely to carry different capacitance or inductance effects, therefore it is hard for a designer to make adaptive modifications comprehensively. Second, the path from an audio codec to an audio output jack on a circuit board is normally long and vulnerable to noise interference; if the resistor 130 is introduced into the design, the output buffer 110 is able to reduce the noise coupling effect through a very low output impedance, but if the resistor 130 is installed, the output buffer 110 might lose its noise-reduction ability consequently. Third, the resistor 130 is usually a passive component of constant resistance on a circuit board; in consideration of so many kinds of sound output devices 120, a designer can hardly match the resistor 130 of constant resistance with all kinds of sound output devices 120, and thus a few cases would be taken care while others would be sacrificed.
People who are interested in the current arts can refer to the U.S. patent application by the following publication number: 20130158921.